Showing papers by "Renée M. Bekker published in 2004"

Dispersal potential in plant communities depends on environmental conditions

Abstract: 1 Local plant communities can only function within a metacommunity context if they are connected by appropriate dispersal vectors, accommodating the transport of propagules between sites. The capacity for long-distance dispersal may be a key factor in the survival of local populations, especially in fragmented landscapes, and hence may have a large impact on local species composition. Dispersal vectors with a large efficiency for long-distance dispersal included in this study are: water, wind, large mammals and birds. 2 We tested the hypothesis that variation in dispersal traits across plant communities is related to the position of the communities along major environmental gradients. This hypothesis was tested for (i) separate long-distance dispersal vectors and (ii) multiple dispersal vectors (the number of potential long-distance dispersal vectors per species). 3 To quantify linkages between dispersal traits and environmental gradients, we coupled a data base containing dispersal attributes with another data base, containing 40 000 local vegetation descriptions aggregated into 123 plant communities. For each dispersal vector, the proportions of species that have access to this vector per community (weighted trait scores) were projected along three major environmental gradients: soil moisture, nutrient availability and light availability. 4 The potential importance of individual dispersal vectors showed clear differences along the three environmental gradients, with the greatest differences along the light availability gradient. The differences in dispersal traits probably reflect environmental constraints on the availability or efficiency of individual dispersal vectors. 5 The ability to be dispersed by multiple dispersal vectors is a common phenomenon in most plant communities (an average of 2.15 vectors per species). The mean number of potential long-distance dispersal vectors per species increases with light availability. This probably implies that plant communities differ in their response to both habitat fragmentation and habitat restoration. 6 Despite differences in trait spectra among communities, all dispersal syndromes are represented in nearly all communities. An important consequence of this complementarity in dispersal traits is that species within the same community may experience different connectivity. 7 The results emphasize the need for dispersal models based upon multiple dispersal vectors that explicitly include parameters for habitat characteristics.

Standaardlijst van de Nederlandse flora 2003

Abstract: The present Standard List is the updated sixth edition in the series ‘Standard List of the Flora of the Netherlands’. Standard Lists have regularly been published since 1971 with intervals of 4 to 8 years and give an up-to-date survey of the vascular plant species occurring in the Netherlands. The present Standard List gives for each species: (1) the taxon code number, (2) the scientific name, (3) the vernacular name in Dutch, (4) the rarity for three periods in the 20th century according to the KFK-scale, (5) the Red List category to which it belongs, (6, 7) the origin and – relevant for non-indigenous species – the period of naturalization, (8, 9) the dispersal and seed bank categories to which it belongs, and (10, 11) the ecological species groups to which it belongs according to two classification systems. The species are arranged in alphabetical order of scientific names. The incorporation of vernacular names, origins and periods of naturalization, and dispersal and seed bank categories is new in this edition of the Standard List. The present Standard List includes 1536 taxa – mainly species and only few subspecies and cultivars –, which is 59 taxa more than the previous Standard List of 1996.

Why Young Coastal Dune Slacks Sustain a High Biodiversity

Abstract: Dune slacks are depressions within coastal dune areas that are flooded during the rainy season, which in Europe is during winter and spring (Boorman et al. 1997; Grootjans et al. 1998), but in the tropics during the summer (Vazquez, Chap 12). During the dry season the water table may drop far below the surface.Young dune slacks that have been formed in a natural way, by sand blowing or natural dune formation (Piotrowska 1988; Zoladeski 1991), are very poor in nutrients and at the same time very species-rich. Various life and growth forms can be present in such slacks: annuals, biennials, perennials, young shrubs and trees (Crawford and Wishart 1966; Ranwell 1972). Dune slack soils are usually calcareous, since they normally originate from recently deposited sands that contain much shell fragments. Dune slacks with acid soils occur in areas where sand has been deposited at the beach with a low initial lime content. Examples are dune areas in parts of Poland (Piotrowska 1988) and the Dutch, German and Danish Wadden Sea Islands, where initial lime contents are low (less than 2 % CaCO3; Petersen 2000) and where precipitation dominates over evaporation. This leads to prominent decalcification processes in the top layer and to rapid acidification (Stuyfzand 1993). In dryer areas where evaporation dominates over precipitation, decalcification processes are less evidently expressed in the vegetation. Flooding frequencies during the wet period are decisive for the plant species composition in such dune areas (Zunzunegui et al. 1998; Munoz-Reinoso 2001). Although many species are now restricted to the coastal area, dune slacks have very few endemic species (Van der Maarel and Van der Maarel-Versluys 1996). Many typical dune slack species can also occur in calcareous fens, fen meadows, and other types of inland wetlands. The restriction of many wetland species to the coastal area is no doubt related to the intensive land use in the mainland areas.